This invention relates to a housing, particularly of a vehicle headlamp, having aeration of an interior space of the housing by use of at least one hole for admission and/or exit of flows of air.
The invention further relates to a method for aerating an interior space of a housing, particularly of a vehicle headlamp, wherein air enters the interior space of the housing via at least one air admission hole and air exits via at least one air exit hole.
German patent documents (DE 33 28 788 A1) and (DE 30 04 413 C2) disclose aerated housings wherein at least two holes having cross sections appropriate for low-pressure gas flows are provided.
In general, these holes are positioned so that ventilation of an inside of a unit takes place when flows around the unit are steady (e.g. relative wind is at a constant vehicular speed, or weather-related wind). By contrast, no exchanges of masses of air or gas take place in ventilated systems when the flow about the unit is steady; such exchanges occur only when there are temporary changes in pressure (e.g. pressure impacts when flow speeds about the unit change). For example, while volume flows of one to several liters per minute are measured in aerated housings, net flow rates are lower by an order of magnitude of one to three in housings that are merely ventilated (essentially owing to oscillating air or gas columns). One consequence of these varying flow rates is that, in proportion to a given flow rate, various contaminants are drawn into such housings via ambient air. Contaminants are introduced that have a corrosive effect on the one hand (e.g. on reflector coatings, etc.), and that have a negative esthetic impact owing to formation of visible deposits, on the other hand. An advantage of having an aerated housing is that esthetically adverse visible condensation can be dried significantly faster (drying) than is the case with ventilated housings because of the higher flow of air. A disadvantage of aerated housings is that, under acute condensation conditions, more condensation generally forms faster in interior spaces thereof than in ventilated housings.
Use of filters to influence a relationship between contamination and drying is known in the art. However these filters must be designed to offer only minimal resistance to flow of air through a unit, since an available pressure differential between aeration holes is very low. Therefore small filters must necessarily be relatively macroporous, but then the finest contaminants (e.g. aerosols) can be filtered out only to a limited extent. A use of appropriate microporous filters would require very large filter cross sections in order to achieve a flow rate necessary for sufficiently rapid drying.
It is an object of this invention to improve a housing having aeration of an interior space thereof, so that an overall contaminant load is reduced and any water deposits can dry quickly.
It is a further object of the invention to provide an improved method for aerating the interior space of a housing such that introduction of contaminants is reduced and introduction of outside air with higher humidity than air in the interior space is reduced.